Conventional rooftop ventilators are used to exhaust hot, unpleasant, and/or turbid gases from indoor areas, such as, for example, bathrooms, kitchens, and industrial workspaces, and allow for air circulation. Ventilation of such gases is especially desirable for the removal of moisture build-up to prevent the rotting of a building's structural members and growth of germs. Conventionally, rooftop ventilators have been unsightly, and have further served as nesting places for birds and insects. In addition, conventional rooftop ventilators have included projecting heights which are too high, multi-piece constructions which are difficult to install and unable to adapt to various roof pitches. Furthermore, rooftop ventilators must be of a sturdy construction to withstand the pressures of shipping and handling.
Conventional rooftop ventilators can be active or passive. Active rooftop ventilators can be powered by an artificial, electric power source and have electric fans or blowers designed to expel a greater airflow. Installation of these active ventilators includes a substantial initial investment due to the cost of the ventilator itself and the electrical wiring necessary for installation. Due to the artificial, electric power source, operation of these active ventilators increases the operating costs of a building. Moreover, the moving parts of the electric fans and blowers, such as the fan blades and rotors, used in the active rooftop ventilators need continual maintenance and repair. In addition, the electric fans and blowers add to the footprint of the ventilators on the roof, which can be especially problematic in residential apartment buildings and commercial apartment buildings where roof space is more limited than on industrial buildings.
Some passive rooftop ventilators can be as simple as louvers that merely allow the escape of heated air. Other passive ventilators utilize a rotating turbine fan that derives its rotational force from wind acting upon a radial array of fan blades. The rotational force creates the negative pressure necessary to vent indoor areas. However, these turbine ventilators typically do not create any negative force in low, i.e., 2 m/s, wind velocity. In addition, in greater wind velocity, the negative pressure created by these turbine ventilators is weak and the turbine ventilators are not able to create a positive pressure to force air into the indoor area as necessary.